1. Field of the Invention
This invention lies in the field of the production of petroleum, gas, viscous oils, tar, sulfur and other minerals from geologic formations by special recovery means.
More particularly, the invention is concerned with the recovery of minerals, such as hydrocarbons, from geologic formations containing very viscous hydrocarbons, by heating the formations, such as by burning part of the hydrocarbons, by injecting pressurized air and igniting the hydrocarbons or by injecting high pressure steam.
Still more particularly, this invention is concerned with the mapping of the subsurface formations as the hydrocarbons are progressively removed from the formation by flowing a recovery fluid through the formation.
Still more particularly this invention is concerned with mapping the flow of the injected fluids as the recovery process progresses, by the use of a seismic source at the surface above the area of recovery and detecting the character of the reflections received at a plurality of points, where the selected fluid injected into the formation is designed to change the reflection coefficient at the top interface of the formation.
2. Background of the Invention
Recent work in seismic prospecting has involved improved methods of analyzing field records of reflections received from reflection at the top of certain formations where there is a condition of gas saturated liquids in the pores of the formation. This situation is conventionally known as "bright spot". So far this has only been applied to the recognition of locations in the earth where this condition pre-exists.
My invention involves the step or steps of injecting a selected fluid into a formation to create this condition, where it did not exist before, so as to make visible by seismic waves the presence, in certain locations in the formation, where such "bright spot" conditions had been generated.